The large scale mining of materials tends to be an energy intensive endeavor. In many opencast mines, a fleet of large mining trucks may operate almost continuously to transport ore and/or overburden from an extraction area to a dump or processing site. Many such mining trucks are operated via diesel-powered engines. Both direct drive diesel engines and diesel-electrical drive systems have been used over the years. As with many other heavy equipment systems, fuel costs for mining trucks can be substantial. Moreover, many mines are located in remote locations, and the costs of transporting fuel to the mine site can add significantly to the operational expense. Even obtaining sufficient fuel supplies can be challenging, regardless of cost. For these and other reasons, engineers in the mining industry and mining equipment manufacturers are continually searching for ways to reduce fuel consumption. Given the historical price volatility of commodities, of which mined materials and petroleum fuels are both examples, as well as variation in geology and topography among mine sites, the economics of supplying and consuming energy for mining activities tends to be complex and variable.
For decades mine operators have experimented with the use of electrical power generated on-site or supplied from a utility grid, to power mining equipment. On-site electrical power generation has similar cost and availability concerns to fueling equipment directly via petroleum fuels. Due to the remoteness of many mines and other factors, supplying electrical power from a grid, even over relatively long distances, has proven consistently advantageous for at least certain mines as compared to reliance on petroleum fuels alone. Electrical power costs can nevertheless vary due to market fluctuations, as well as varying from mine to mine depending upon regional availability of fossil fuels, geothermal or hydroelectrical power, or other native or obtainable sources of energy for electricity generation. Thus, even where electrical powering of mining equipment is viable, there remains ample motivation to use it as efficiently as possible, both to control costs and optimize predictability in the face of uncertain economics.
While first proposed decades ago, one contemporary example of the use of electrical power at mine sites is a trolley system having an overhead trolley line to provide electrical power to assist mining trucks, particularly when traveling loaded upon uphill grades. Many opencast mines include a haul road extending from an extraction site for ore to a remote dump site or processing location. The mining trucks used at such sites may need to travel an uphill grade on the haul road that is several kilometers long, or possibly even longer. It will be appreciated that the use of diesel or other petroleum fuels to propel mining trucks carrying literally hundreds of tons of ore up such grades can be quite costly, and thus trolley systems have received renewed interest in recent years.
In addition to drawing power from an overhead trolley line, many different strategies have been proposed for capturing energy used in retarding mining trucks. In particular, certain mining trucks are equipped with onboard energy storage, such that electrical energy regenerated during braking the vehicle can be stored for later use. U.S. Pat. No. 5,351,775 to Johnston et al. is directed to an apparatus and methodology for powering and controlling diesel-electrical off-road haulers, in which hauler drive wheels are propelled and retarded by DC motors. Johnston et al. propose the use of thyristor-type converters to supply current generated by wheel motors in a retarding mode to make possible the use of the electrical power to replace load requirements on a diesel engine of the vehicle. It appears that the strategy proposed by Johnston et al. might be applicable to instances where the diesel engine is ordinarily driven to provide power for loads on the vehicle which cannot otherwise be accommodated by power from a trolley line. Still other strategies propose storing electrical energy on-board, and transferring excess electrical energy to a power grid once on-board energy storage devices are fully charged. There are various disadvantages associated with known regeneration and power distribution strategies.